Pure Monopolies and Natural Monopolies
Pure Monopolies
 
A pure monopoly is a firm that satisfies the following conditions:
- It is the only supplier in the market.
 
- There is no close substitute to the output good.
 
- There is no threat of competition.
 
 
In practice, pure monopolies are very rare.  For instance, a supermarket may be 
the only food supplier in a particular town, but if it raises its prices and 
retains too much of a profit, a competitor may enter the space.  Even the threat 
of serious competition entering the 
market forces the existing firm to 
act conscionably, and differently from how it would act otherwise.  A train 
company may be the only carrier in a particular station, but if cars are also 
available in the area, there exists a close substitute to the output good.
Natural Monopoly
 
A natural monopoly is a firm with such extreme economies of scale that 
once it begins creating a certain level of output, it can produce more at a far 
lower cost than any smaller competitor.  Natural monopolies exist far more 
frequently than pure monopolies, mainly because the requirements are not as 
stringent.  
 
Natural monopolies occur when, for whatever reason, the average cost curves 
decline over a relevant span of output quantities.  A firm with high fixed costs 
relative to its marginal costs 
will have declining average costs 
for a significant span of quantities.  A firm with a decreasing marginal cost 
structure will also have declining average costs.  For example, utilities and 
software are two industries where natural monopolies occur often.
 
An Example
 
A monopoly differs from competitive firms in that it is not a price taker.  
Because it is the only supplier in the market, it faces a downward sloping 
demand curve, the market demand curve.  As a result, the monopoly is free to 
choose its price and quantity according to market demand.  
 
Monopolies are still profit maximizing firms and are thus going to satisfy the 
profit maximizing condition that marginal cost equal marginal 
revenue.  The key to 
understanding monopolies and monopoly power is the marginal revenue 
calculation.  In a perfectly competitive market, there exists a market 
price.  Marginal revenue is simply 
equal to price in this market; every additional unit that is sold brings the 
market price.  In a monopoly, however, every quantity is associated with a 
different price.  The marginal revenue is not simply the price.